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Speech dereverberation aims to alleviate the negative impact of late reverberant reflections. The weighted prediction error (WPE) method is a well-established technique known for its superior performance in dereverberation. However, in scenarios where microphone nodes are dispersed, the centralized approach of the WPE method requires aggregating all observations for inverse filtering, resulting in a significant computational burden. This paper introduces a distributed speech dereverberation method that emphasizes low computational complexity at each node. Specifically, we leverage the distributed adaptive node-specific signal estimation (DANSE) algorithm within the multichannel linear prediction (MCLP) process. This approach empowers each node to perform local operations with reduced complexity while achieving the global performance through inter-node cooperation. Experimental results validate the effectiveness of our proposed method, showcasing its ability to achieve efficient speech dereverberation in dispersed microphone node scenarios.

Personal sound zone (PSZ) systems, which aim to create listening (bright) and silent (dark) zones in neighboring regions of space, are often based on time-varying acoustics. Conventional adaptive-based methods for handling PSZ tasks suffer from the collection and processing of acoustic transfer functions~(ATFs) between all the matching microphones and all the loudspeakers in a centralized manner, resulting in high calculation complexity and costly accuracy requirements. This paper presents a distributed pressure-matching (PM) method relying on diffusion adaptation (DPM-D) to spread the computational load amongst nodes in order to overcome these issues. The global PM problem is defined as a sum of local costs, and the diffusion adaption approach is then used to create a distributed solution that just needs local information exchanges. Simulations over multi-frequency bins and a computational complexity analysis are conducted to evaluate the properties of the algorithm and to compare it with centralized counterparts.

High-velocity atomic clouds in the Galactic center have attracted significant attention due to their enigmatic formation process, which is potentially linked to the starburst or supermassive black hole activities in the region. Further, the discovery of high-velocity molecular clouds (HVMCs) presents a greater puzzle, because they are much denser and more massive. If the HVMCs were accelerated by the strong activities in the Galactic center, they are expected to be destroyed before they reach such a high velocity. To shed light on this phenomenon, we perform three-dimensional numerical simulations to investigate the origin and hydrodynamic evolution of HVMCs during a starburst in the Galactic center. We find that the presence of a magnetic field provides effective protection and acceleration to molecular clouds (MCs) within the galactic winds. Consequently, the MCs can attain latitudes of approximately 1 kpc with velocities around 200 km/s, consistent with the observed characteristics of HVMCs. The consistency of our findings across a wide parameter space supports the conclusion that HVMCs can indeed withstand the starburst environment in the Galactic center, providing valuable insights into their survival mechanisms., Comment: 18 pages, 16 figures, submitted to MNRAS

We perform three-dimensional numerical simulations to study the hydrodynamic evolution of Sgr A East, the only known supernova remnant (SNR) in the center of our Galaxy, to infer its debated progenitor SN type and its potential impact on the Galactic center environment. Three sets of simulations are performed, each of which represents a represent a certain type of SN explosion (SN Iax, SN Ia or core-collapse SN) expanding against a nuclear outflow of hot gas driven by massive stars, whose thermodynamical properties have been well established by previous work and fixed in the simulations. All three simulations can simultaneously roughly reproduce the extent of Sgr A East and the position and morphology of an arc-shaped thermal X-ray feature, known as the "ridge". Confirming previous work, our simulations show that the ridge is the manifestation of a strong collision between the expanding SN ejecta and the nuclear outflow. The simulation of the core-collapse SN, with an assumed explosion energy of 5x10^50 erg and an ejecta mass of 10 M_sun, can well match the X-ray flux of the ridge, whereas the simulations of the SN Iax and SN Ia explosions underpredict its X-ray emission, due to a smaller ejecta mass. All three simulations constrain the age of Sgr A East to be <1500 yr and predict that the ridge should fade out over the next few hundred years. We address the implications of these results for our understanding of the Galactic center environment., Comment: 21 pages, 18 figures. Accepted for publication on MNRAS

Elemental abundances are key to our understanding of star formation and evolution in the Galactic center. Previous work on this topic has been based on infrared (IR) observations, but X-ray observations have the potential of constraining the abundance of heavy elements, mainly through their K-shell emission lines. Using 5.7 Ms Chandra observations, we provide the first abundance measurement of Si, S, Ar, Ca and Fe, in four prominent diffuse X-ray features located in the central parsec of the Galaxy, which are the manifestation of shock-heated hot gas. A two-temperature, non-equilibrium ionization spectral model is employed to derive the abundances of these five elements. In this procedure, a degeneracy is introduced due to uncertainties in the composition of light elements, in particular, H, C and N. Assuming that the hot gas is H-depleted but C- and N-enriched, as would be expected for a standard scenario in which the hot gas is dominated by Wolf-Rayet star winds, the spectral fit finds a generally subsolar abundance for the heavy elements. If, instead, the light elements had a solar-like abundance, the heavy elements have a fitted abundance of $\sim$1--2 solar. The $\alpha$/Fe abundance ratio, on the other hand, is mostly supersolar and insensitive to the exact composition of the light elements. These results are robust against potential biases due to either a moderate spectral S/N or the presence of non-thermal components. Implications of the measured abundances for the Galactic center environment are addressed., Comment: 13 pages, 6 figures, Accepted for publication in MNRAS

The youngest Galactic supernova remnant G1.9+0.3 shows a discrete feature between its radio and X-ray morphologies. The observed radio morphology features a single maximum in the north, while the X-ray observation shows two opposite 'ears' on the east and west sides. Using 3D magneto hydrodynamical simulations, we investigate the formation of the discrete feature of the remnant. We have tested different parameters for better simulation and reproduced similar discrete features under an environment with density gradient and an environment with clump, which provides a possible explanation of the observation., Comment: 7 pages, 3 figures, accepted for publication in ApJ

Globular clusters (GCs) are thought to harbor the long-sought population of intermediate-mass black holes (IMBHs). We present a systematic search for a putative IMBH in 81 Milky Way GCs, based on archival Chandra X-ray observations. We find in only six GCs a significant X-ray source positionally coincident with the cluster center, which have 0.5-8 keV luminosities between $\sim1\times 10^{30}~{\rm erg~s^{-1}}$ to $\sim 4\times10^{33}~{\rm erg~s^{-1}}$. However, the spectral and temporal properties of these six sources can also be explained in terms of binary stars. The remaining 75 GCs do not have a detectable central source, most with $3\sigma$ upper limits ranging between $10^{29-32}~{\rm erg~s^{-1}}$ over 0.5-8 keV, which are significantly lower than predicted for canonical Bondi accretion. To help understand the feeble X-ray signature, we perform hydrodynamic simulations of stellar wind accretion onto a $1000~{\rm M_\odot}$ IMBH from the most-bound orbiting star, for stellar wind properties consistent with either a main-sequence (MS) star or an asymptotic giant branch (AGB) star. We find that the synthetic X-ray luminosity for the MS case ($\sim 10^{19}\rm~erg~s^{-1}$) is far below the current X-ray limits. The predicted X-ray luminosity for the AGB case ($\sim 10^{34}\rm~erg~s^{-1}$), on the other hand, is compatible with the detected central X-ray sources, in particular the ones in Terzan 5 and NGC 6652. However, the probability of having an AGB star as the most-bound star around the putative IMBH is very low. Our study strongly suggests that it is very challenging to detect the accretion-induced X-ray emission from IMBHs, even if they were prevalent in present-day GCs., Comment: 21 pages, 10 figures, accepted by MNRAS

A pair of non-thermal radio bubbles recently discovered in the inner few hundred parsecs of the Galactic center bears a close spatial association with elongated, thermal X-ray features called the X-ray chimneys. While their morphology, position, and orientation vividly point to an outflow from the Galactic center, the physical processes responsible for the outflow remain to be understood. We use three-dimensional magnetohydrodynamic simulations to test the hypothesis that the radio bubbles/X-ray chimneys are the manifestation of an energetic outflow driven by multiple core-collapsed supernovae in the nuclear stellar disk, where numerous massive stars are known to be present. Our simulations are run with different combinations of two main parameters, the supernova birth rate and the strength of a global magnetic field being vertically oriented with respect to the disk. The simulation results show that a hot gas outflow can naturally form and acquire a vertically elongated shape due to collimation by the magnetic pressure. In particular, the simulation with an initial magnetic field strength of 80 $\mu$G and a supernova rate of 1 $kyr^{-1}$ can well reproduce the observed morphology, internal energy and X-ray luminosity of the bubbles after an evolutionary time of 330 kyr. On the other hand, a magnetic field strength of 200 $\mu$G gives rise to an overly elongated outflow that is inconsistent with the observed bubbles. The simulations also reveal that, inside the bubbles, mutual collisions between the shock waves of individual supernovae produce dense filaments of locally amplified magnetic field. Such filaments may account for a fraction of the synchrotron-emitting radio filaments known to exist in the Galactic center., Comment: 20 pages, 10 figures, accepted by ApJ

Recent hydrodynamic simulations and observations of radio jets have shown that the surrounding environment has a large effect on their resulting morphology. To investigate this we use a sample of 50 Extended Radio Active Galactic Nuclei (ERAGN) detected in the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. These sources are all successfully cross-identified to galaxies within a redshift range of $0.55 \leq z \leq 1.35$, either through spectroscopic redshifts or accurate photometric redshifts. We find that ERAGN are more compact in high-density environments than those in low-density environments at a significance level of 4.5$\sigma$. Among a series of internal properties under our scrutiny, only the radio power demonstrates a positive correlation with their spatial extent. After removing the possible radio power effect, the difference of size in low- and high-density environments persists. In the global environment analyses, the majority (86\%) of high-density ERAGN reside in the cluster/group environment. In addition, ERAGN in the cluster/group central regions are preferentially compact with a small scatter in size, compared to those in the cluster/group intermediate regions and fields. In conclusion, our data appear to support the interpretation that the dense intracluster gas in the central regions of galaxy clusters plays a major role in confining the spatial extent of radio jets.

A small cluster of massive stars residing in the Galactic center, collectively known as IRS13E, is of special interest due to its close proximity to Sgr A* and the possibility that an embedded intermediate-mass black hole (IMBH) binds its member stars. It has been suggested that colliding winds from two member stars, both classified as Wolf-Rayet type, are responsible for the observed X-ray, infrared and radio emission from IRS13E. We have conducted an in-depth study of the X-ray spatial, temporal and spectral properties of IRS13E, based on 5.6 Ms of ultra-deep Chandra observations obtained over 20 years. These X-ray observations show no significant evidence for source variability. We have also explored the kinematics of the cluster members, using Keck near-infrared imaging and spectroscopic data on a 14-yr baseline that considerably improve the accuracy of stars' proper motions. The observations are interpreted using 3-dimensional hydrodynamical simulations of colliding winds tailored to match the physical conditions of IRS13E, leading us to conclude that the observed X-ray spectrum and morphology can be well explained by the colliding wind scenario, in the meantime offering no support for the presence of a putative IMBH. An IMBH more massive than a few $10^3{\rm~M_\odot}$ is also strongly disfavored by the stellar kinematics., Comment: 24 pages, 9 figures, Accepted for publication in Astrophysical Journal

We investigate the relation between the optical extinction ($A_V$) and the hydrogen column density ($N_H$) determined from X-ray observations of a large sample of Galactic sightlines toward 35 supernova remnants, 6 planetary nebulae, and 70 X-ray binaries for which $N_H$ was determined in the literature with solar abundances. We derive an average ratio of ${N_H}/{A_V}=(2.08\pm0.02)\times10^{21}{\rm H\, cm^{-2}\, mag^{-1}}$ for the whole Galaxy. We find no correlation between ${N_H}/{A_V}$ and the number density of hydrogen, the distance away from the Galactic centre, and the distance above or below the Galactic plane. The ${N_H}/{A_V}$ ratio is generally invariant across the Galaxy, with ${N_H}/{A_V}=(2.04\pm0.05)\times10^{21}{\rm H\, cm^{-2}\, mag^{-1}}$ for the 1st and 4th Galactic quadrants and ${N_H}/{A_V}=(2.09\pm0.03)\times10^{21}{\rm H\, cm^{-2}\, mag^{-1}}$ for the 2nd and 3rd Galactic quadrants. We also explore the distribution of hydrogen in the Galaxy by enlarging our sample with additional 74 supernova remnants for which both $N_H$ and distances are known. We find that, between the Galactic radius of 2 kpc to 10 kpc, the vertical distribution of hydrogen can be roughly described by a Gaussian function with a scale height of $h=75.5\pm12.4\,{\rm pc}$ and a mid-plane density of $n_{H}(0)=1.11\pm0.15\,{\rm cm^{-3}}$, corresponding to a total gas surface density of ${\sum}_{gas}{\sim}7.0\,{M_{\bigodot}}\,{\rm pc^{-2}}$. We also compile $N_H$ from 19 supernova remnants and 29 X-ray binaries for which $N_H$ was determined with subsolar abundances. We obtain ${N_H}/{A_V}=(2.47\pm0.04)\times10^{21}{\rm H\, cm^{-2}\, mag^{-1}}$ which exceeds that derived with solar abundances by $\sim$20%. We suggest that in future studies one may simply scale $N_H$ derived from subsolar abundances by a factor of $\sim$1.2 when converting to $N_H$ of solar abundances., Comment: 32 pages, 10 figures, 7 tables; accepted for publication in MNRAS